Detection of H2O2 at the Nanomolar Level by Electrode Modified with Ultrathin AuCu Nanowires

Nuclear matrix protein 22 in bladder cancer

Bladder cancer (BC) is ranked as the ninth most common malignancy worldwide, with approximately 570,000 new cases reported annually and over 200,000 deaths. Cystoscopy remains the gold standard for the diagnosis of BC, however, its invasiveness, cost, and discomfort have driven the demand for the development of non-invasive, cost-effective alternatives. Nuclear matrix protein 22 (NMP22) is a promising non-invasive diagnostic tool, having received FDA approval. Traditional methods for detecting NMP22 require a laboratory environment equipped with specialized equipment and trained personnel, thus, the development of NMP22 detection devices holds substantial potential for application. In this review, we evaluate the NMP22 sensors developed over the past decade, including electrochemical, colorimetric, and fluorescence biosensors. These sensors have enhanced detection sensitivity and overcome the limitations of existing diagnostic methods. However, many emerging devices exhibit deficiencies that limit their potential clinical use, therefore, we propose how sensor design can be optimized to enhance the likelihood of clinical translation and discuss the future applications of NMP22 as a legacy biomarker, providing insights for the design of new sensors.

Growth pathways of Cu shells on Au and AuCu seeds: interdiffusion, shape transformations, strained shells and patchy surfaces

The growth of AuCu nanoparticles obtained by depositing Cu atoms on starting seeds of pure Au and on mixed AuCu seeds is studied by molecular dynamics simulations. Depending on the shape of the seed, its composition and the growth temperature, different growth pathways are observed, in which several types of structural transformations take place. The final growth structures comprise Au@Cu core@shell arrangements as well as Janus-like structures with patchy surfaces. The results of the growth simulations are rationalized in terms of the activation of different diffusion processes, both on the surface and inside the growing clusters. These diffusion processes regulate structural transitions between different motifs and the occurrence of dewetting phenomena. The simulation results show that depositon of Cu atoms on pure Au or mixed AuCu seed can be an effective tool for producing clusters with uncommon surface atom arrangements of potential interest for catalysis.

Phosphate-driven H2O2 decomposition on DNA-bound bio-inspired activated carbon-based sensing platform for biological and food samples

Hydrogen peroxide (H₂O₂) is one of the most important reactive oxygen species (ROS). Increased endogenous H₂O₂ levels indicate oxidative stress and could be a potential marker of many diseases, including Alzheimer's, cardiovascular diseases, and diabetes. However, consuming H₂O_2-incorporated food has adverse effects on humans and is a serious health concern. We used salmon testes DNA with bio-inspired activated carbon (AC) as an electrocatalyst for developing a novel H₂O₂ sensor. The phosphate backbone of DNA contains negatively charged oxygen groups that specifically attract protons from H₂O₂ reduction. We observed a linearity range of 0.01-250.0 μM in the H₂O₂ reduction peak current with a detection limit of 2.5 and 45.7 nM for chronoamperometric and differential pulse voltammetric studies. High biocompatibility of the sensor was achieved by the DNA, facilitating endogenous H₂O₂ detection. Moreover, this non-enzymatic sensor could also help in the rapid screening of H₂O₂-contaminated foods.

Microporous PdCuB nanotag-based electrochemical aptasensor with Au@CuCl2 nanowires interface for ultrasensitive detection of PD-L1-positive exosomes in the serum of lung cancer patients

Programmed cell death ligand 1 protein-positive (PD-L1⁺) exosomes have been found to be a potential biomarker for the diagnosis of non-small cell lung cancer (NSCLC). However, the development of highly sensitive detection technique for PD-L1⁺ exosomes is still a challenge in clinical applications. Herein, a sandwich electrochemical aptasensor based on ternary metal-metalloid palladium-copper-boron alloy microporous nanospheres (PdCuB MNs) and Au@CuCl₂ nanowires (NWs) was designed for the detection of PD-L1⁺ exosomes. The excellent peroxidase-like catalytic activity of PdCuB MNs and the high conductivity of Au@CuCl₂ NWs endow the fabricated aptasensor with intense electrochemical signal, thus enabling the detection of low abundance exosomes. The analytical results revealed that the aptasensor maintained favorable linearity over a wide concentration range of 6 orders of magnitude and reached a low detection limit of 36 particles/mL. The aptasensor is successfully applied to the analysis of complex serum samples and achieves the accurate identification of clinical NSCLC patients. Overall, the developed electrochemical aptasensor provides a powerful tool for early diagnosis of NSCLC.

Laser-assisted surface activation for fabrication of flexible non-enzymatic Cu-based sensors

A rapid and effective technique has been develped for the fabrication of sensor-active copper-based materials on the surface of such flexible polymers as terephthalate, polyethylene naphthalate, and polyimide using the method of laser surface modification. For this purpose, we optimized the polymer surface activation parameters using laser sources with a picosecond pulse duration for subsequent selective metallization within the activated region. Furthermore, the fabricated copper structures were modified with gold nanostructures and by electrochemical passivation to produce copper-gold and oxide-containing copper species, respectively. As a result, in comparison with pure copper electrodes, these composite materials exhibit much better electrocatalytic performance concerning the non-enzymatic identification of biologically important disease markers such as glucose, hydrogen peroxide, and dopamine.

Electrodes and electrocatalysts for electrochemical hydrogen peroxide sensors: a review of design strategies

H₂O₂ sensing is required in various biological and industrial applications, for which electrochemical sensing is a promising choice among various sensing technologies. Electrodes and electrocatalysts strongly influence the performance of electrochemical H₂O₂ sensors. Significant efforts have been devoted to electrode nanostructural designs and nanomaterial-based electrocatalysts. Here, we review the design strategies for electrodes and electrocatalysts used in electrochemical H₂O₂ sensors. We first summarize electrodes in different structures, including rotation disc electrodes, freestanding electrodes, all-in-one electrodes, and representative commercial H₂O₂ probes. Next, we discuss the design strategies used in recent studies to increase the number of active sites and intrinsic activities of electrocatalysts for H₂O₂ redox reactions, including nanoscale pore structuring, conductive supports, reducing the catalyst size, alloying, doping, and tuning the crystal facets. Finally, we provide our perspectives on the future research directions in creating nanoscale structures and nanomaterials to enable advanced electrochemical H₂O₂ sensors in practical applications.

Nanowire-based sensor electronics for chemical and biological applications

Detection and recognition of chemical and biological species via sensor electronics are important not only for various sensing applications but also for fundamental scientific understanding. In the past two decades, sensor devices using one-dimensional (1D) nanowires have emerged as promising and powerful platforms for electrical detection of chemical species and biologically relevant molecules due to their superior sensing performance, long-term stability, and ultra-low power consumption. This paper presents a comprehensive overview of the recent progress and achievements in 1D nanowire synthesis, working principles of nanowire-based sensors, and the applications of nanowire-based sensor electronics in chemical and biological analytes detection and recognition. In addition, some critical issues that hinder the practical applications of 1D nanowire-based sensor electronics, including device reproducibility and selectivity, stability, and power consumption, will be highlighted. Finally, challenges, perspectives, and opportunities for developing advanced and innovative nanowire-based sensor electronics in chemical and biological applications are featured.

One-Step Preparation of Nitrogen-Doped Graphene Quantum Dots With Anodic Electrochemiluminescence for Sensitive Detection of Hydrogen Peroxide and Glucose

Simple and efficient synthesis of graphene quantum dots (GQDs) with anodic electrochemiluminescence (ECL) remains a great challenge. Herein, we present an anodic ECL-sensing platform based on nitrogen-doped GQDs (N-GQDs), which enables sensitive detection of hydrogen peroxide (H₂O₂) and glucose. N-GQDs are easily prepared using one-step molecular fusion between carbon precursor and a dopant in an alkaline hydrothermal process. The synthesis is simple, green, and has high production yield. The as-prepared N-GQDs exhibit a single graphene-layered structure, uniform size, and good crystalline. In the presence of H₂O₂, N-GQDs possess high anodic ECL activity owing to the functional hydrazide groups. With N-GQDs being ECL probes, sensitive detection of H₂O₂ in the range of 0.3–100.0 μM with a limit of detection or LOD of 63 nM is achieved. As the oxidation of glucose catalyzed by glucose oxidase (GOx) produces H₂O₂, sensitive detection of glucose is also realized in the range of 0.7–90.0 μM (LOD of 96 nM).

Ni and Co synergy in bimetallic nanowires for the electrochemical detection of hydrogen peroxide

The development of a highly sensitive and selective non-enzymatic electrode catalyst for the detection of a target molecule was remained a great challenge. In this regard, bimetallic nanowires (BMNWs) are considered as promising electrode material for their fascinating physical/chemical properties superior to a single system. In this article, nickel cobalt (Ni _x -Co) BMNWs with tunable stoichiometry were prepared by a template assisted electrodeposition method and their catalytic performance was investigated for the detection of hydrogen peroxide (H₂O₂). It has been found that Ni-Co (0.5:1) BMNWs/PC electrode exhibits superior non-enzymatic sensing ability toward H₂O₂ detection with a high selectivity. The electrode shows fast response within ∼3 s and an excellent reproducible sensitivity of 2211.4 μAmM^-1 cm^-2, which is the best compared to the individual Ni, Co, Ni-Co (0.3:1) BMNWs and previously reported electrodes. In addition, the electrode shows a linear response in the wide concentration range from 0.005 mM to 9 mM, low detection limit of 0.5 μM (S/N = 3.2) and a relatively long-term storage (50 d). Moreover, the sensor reveals excellent results for H₂O₂ detection in the real samples. The enhanced sensitivity of the Ni-Co (0.5:1) BMNWs based electrode may be due to the stable structure and synergy of Ni and Co. The results demonstrate that the catalytic activity of the electrode binary catalyst towards H₂O₂ detection can be improved by adjusting the Ni/Co ratio in BMNWs. The excellent performance of the electrode suggests that Ni-Co BMNWs are promising candidate for the construction of cost-effective electrochemical sensors for medical and industrial applications.

Highly branched gold-copper nanostructures for non-enzymatic specific detection of glucose and hydrogen peroxide

The development of highly sensitive and highly selective sensors for non-enzymatic glucose and hydrogen peroxide (H₂O₂) detection using gold-copper alloy nanoparticles (AuCu alloy NPs) is reported. The AuCu NPs are nanostructures with branches and can be used as an electrochemical catalyst. Series of AuCu alloy NPs with various metal ratios are synthesized through a coreduction reaction. The morphology of AuCu alloy NPs is altered from highly branched structures (nanourchin, nanobramble, nanostar, nanocrystal) to a spherical shape by increasing Au content in the synthesis reaction. Cu-rich AuCu nanobramble and Au-rich AuCu nanostar exhibit selective electrocatalysis behaviors toward electro-oxidation of glucose and electroreduction of H₂O₂, respectively. The AuCu nanobramble-based sensor holds great potential in glucose detection with a linear working range of 0.25 to 10 mM. The sensor possesses a sensitivity of 339.35 μA mM^-1 cm^-2, a limit of detection (LOD) of 16.62 μM, which is an acceptable selectivity and good stability. In addition, the AuCu nanostar-based sensor shows excellent electrochemical responses toward H₂O₂ reduction with good selectivity, reproducibility, and a short response time of about 2-3 s. The linear range for H₂O₂ determination is 0.05 to 10 mM, with LOD and sensitivity of 10.93 μM and 133.74 μA mM^-1 cm^-2, respectively. The good sensing performance is a result of the synergistic surface structure and atomic composition effects, which leads AuCu alloys to be a promising nanocatalyst for sensing both glucose and H₂O₂. Graphical abstract Schematic illustration presents the construction of gold-copper alloy nanoparticles (AuCu alloy NPs) on the surface of screen-printed carbon electrode (SPCE). The highly branched nanostructures of AuCu alloys with different surface structure and metal ratios give selective electrocatalysis behaviors. Cu-rich AuCu nanobramble-based sensor reveals prominent electrocatalytic activity for glucose detection. Au-rich AuCu nanostar-based sensor provides good electrochemical response for H₂O₂ detection.

Voltammetric determination of hydrogen peroxide using AuCu nanoparticles attached on polypyrrole-modified 2D metal-organic framework nanosheets

AuCu/PPy/Cu-TCPP nanocomposites were synthesized by attaching AuCu nanoparticles to a polypyrrole (PPy)-modified 2D Cu-TCPP metal-organic framework nanosheet; Cu-TCPP can exhibit catalytic activity for the reduction of H₂O₂. Based on the nanocomposite, a new method for the determination of H₂O₂ was established. The morphology of the AuCu/PPy/Cu-TCPP was analyzed by transmission electron microscopy. Cu-TCPP exhibited a 2D nanosheet with obvious wrinkles, and a large amount of AuCu was uniformly attached to PPy/Cu-TCPP. The composition and structure were studied by X-ray diffraction, FTIR, and X-ray photoelectron spectroscopy. At the optimal working potential and scan rate of - 0.55 V(vs. SCE) and 100 mV/s, respectively, electrochemical studies indicated that in N₂-saturated supporting electrolyte, the method showed good catalytic performance for H₂O₂, with a detection limit of 6.67 nM (S/N = 3), a linear range of 7.10 μM-24.10 mM, and a sensitivity of 35.0 μA mM^-1 cm². Compared to H₂O₂ methods based on related materials, this method exhibits a wide linear range, and the detection limit is down to nanomolar. Graphical abstract Schematic presentation of the preparation of AuCu/PPy/Cu-TCPP nanocomposites. AuCu/PPy/Cu-TCPP nanocomposite was prepared by loading gold-copper (AuCu) bimetallic nanoparticles with good catalytic properties on two-dimensional copper (II)-porphyrin (Cu-TCPP) nanosheet metal-organic framework material, whose conductivity was improved by polypyrrole (PPy). A method for the determination of hydrogen peroxide by voltammetric was established.

Highly dispersive Pt-Pd nanoparticles on graphene oxide sheathed carbon fiber microelectrodes for electrochemical detection of H2O2 released from living cells

We report a facile strategy for the synthesis of surfactant-free, small and highly dispersive Pt-Pd nanoparticles on graphene oxide (Pt-Pd NPs/GO) by an electroless deposition method, which is sheathed on carbon fiber microelectrodes (CFMs) as an electrochemical sensing platform for highly sensitive and selective detection of hydrogen peroxide (H₂O₂) released from the living cells. GO serves as the reducing agent and stabilizer for electroless deposition of Pd NPs on the surface of GO owing to its low work function (4.38 eV) and highly conjugated electronic structure. The obtained Pd NPs/GO have a relatively high work function (4.64 eV), and thereby could be used as stabilizer for synthesis of surfactant-free, small and highly dispersive Pt-Pd NPs/GO by chemical reduction of K₂PtCl₄. The obtained Pt-Pd NPs have a uniform size of 4.0 ± 0.6 nm on the surface of GO. Moreover, the Pt-Pd NPs/GO sheathed CFMs exhibit an excellent electrocatalytic activity for the reduction of H₂O₂ with a low detection limit of 0.3 μM and good selectivity. These good properties enable the modified microelectrode to detect the H₂O₂ released from living cells.

Controlled Fabrication of Flower-Shaped Au-Cu Nanostructures Using a Deep Eutectic Solvent and Their Performance in Surface-Enhanced Raman Scattering-Based Molecular Sensing

Controlled synthesis of anisotropic bimetallic nanostructures with tunable morphology is of great current interest for their applications in surface-enhanced Raman scattering (SERS), plasmonics, and catalysis. Despite huge effort that has been devoted so far, fabrication of bimetallic nanostructures with controlled morphology and size remained to be a great challenge, especially when their shapes are anisotropic. Here, we report a facile, one-step synthetic approach for the fabrication of anisotropic bimetallic gold-copper nanostructures (Au-Cu NSs) of the 200-300 nm size range, using choline chloride/urea (ChCl/urea)-based deep eutectic solvent (DES) as the soft template. A concentration of the CuCl₂ precursor in the reaction mixture was found to impact the reduction kinetics of the metal ions, directly affecting the final morphology of the Au-Cu nanostructures and elemental distributions in them. The fabricated anisotropic Au-Cu NSs revealed a high SERS signal for crystal violet (CV) molecules adsorbed at their surfaces, with the signal enhancement factor as high as 0.21 × 10⁶ and capacity of detecting CV molecules of concentrations as low as 10^-10 M in their aqueous solutions. The growth mechanism of the anisotropic bimetallic nanostructures in DES and their SERS performance has been discussed. The simple DES-assisted synthesis strategy presented in this work can be adopted for large-scale nonaqueous fabrication of other bimetallic nanostructures in a quite "greener" way.

Oxygen vacancy confined nickel cobaltite nanostructures as an excellent interface for the enzyme-free electrochemical sensing of extracellular H2O2 secreted from live cells

Oxygen vacancy (O_V) manufacturing is an effective way to boost the efficiency of a catalyst; therefore, the development of O_V-rich catalysts has attracted substantial research interest.

Fabrication of hexahedral Au-Pd/graphene nanocomposites biosensor and its application in cancer cell H2O2 detection

Currently, real time monitoring of chemical substances in vivo and in vitro has gained enormous attraction, and many researches reports have been focused on the design and construction of high-performance biosensor devices. In this work, a high-performance sensor was constructed by taking advantage of the excellent electrochemical activity and high-index facets of Au-Pd nanocubes and the large surface of rGO. Glassy carbon electrodes (GCEs) were modified by both Au-Pd nanocubes and rGO nanocomposites via physical adsorption. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were utilized to characterize and identify this unique nanostructure. These three-dimensional nanocomposites possess a high electroactive surface area and an excellent electrical conductivity, which resulted in favorable electroreduction activity toward H₂O₂ with a lower detection limit of 4 nM, a wide linear range from 0.005 μM to 3.5 mM and a rapid response time. Furthermore, the proposed sensor exhibited desirable performance in the detection of endogenous H₂O₂ in human serum samples and real-time monitoring of H₂O₂ released from living breast cancer cell lines. In summary, this work not only provides a potential method to construct a physiological and pathological H₂O₂ biosensor but also makes a valuable contribution to the early diagnosis of different cancers.

Facile Solvothermal Preparation of Mn2CuO4 Microspheres: Excellent Electrocatalyst for Real-Time Detection of H2O2 Released from Live Cells

Hydrogen peroxide (H₂O₂) is an eminent biomarker in pathogenesis; a selective, highly sensitive real-time detection of H₂O₂ released from live cells has drawn a significant research interest in bioanalytical chemistry. Binary transition-metal oxides (BTMOs) displayed a recognizable benefit in enhancing the sensitivity of H₂O₂ detection; although the reported BTMO-based H₂O₂ sensor's detection limit is still insufficient, it is not appropriate for in situ profiling of trace amounts of cellular H₂O₂. In this paper, we describe an efficient, reliable electrochemical biosensor based on Mn₂CuO₄ (MCO) microspheres to assay cellular H₂O₂. The Mn₂CuO₄ microspheres were prepared through a superficial solvothermal method. It is obvious from impedance studies, introduction of manganese into copper oxide lattice significantly improved the ionic conductivity, which is beneficial for the electrochemical sensing process. Thanks to the distinct microsphere structure and excellent synergy, MCO-modified electrode exhibited excellent nonenzymatic electrochemical behavior toward H₂O₂ sensing. The MCO-modified electrode delivered a broad working range (36 nM to 9.3 mM) and an appreciable detection limit (13 nM), with high selectivity toward H₂O₂. To prove its practicality, the developed sensor was applied in the detection of cellular H₂O₂ released by RAW 264.7 cells in presence of CHAPS. These results label the possible appliance of the sensor in clinical analysis and pathophysiology. Thus, BTMOs are evolving as a promising candidate in designing catalytic matrices for biosensor applications.

A label-free immunosensor for the detection of nuclear matrix protein-22 based on a chrysanthemum-like Co-MOFs/CuAu NWs nanocomposite

In this study, a new, simple, and label-free electrochemical immunosensor was presented for the detection of nuclear matrix protein-22 (NMP-22). In order to accurately monitor very small amounts of NMP-22, it was advantageous to use highly efficient nanomaterials as signals. For this reason, we synthesized a chrysanthemum-like nanocomposite (Co-MOFs/CuAu NWs), using Co-based metal-organic frameworks (Co-MOFs) as carriers and copper gold nanowires (CuAu NWs) wrapped around their surface, which was applied for modifying a glassy carbon electrode (GCE). The Co-MOFs/CuAu NWs possessed outstanding catalytic capabilities, which served as signal materials and simultaneously carried the anti-NMP-22 antibody (Ab). When different concentrations of the NMP-22 antigen (Ag) were specifically attached to the immunosensor, the current responses decreased by varying degrees. The designed biosensor used the principle to establish a linear regression equation and achieve an accurate quantification of NMP-22. After optimization, the NMP-22 sensor exhibited a good linear response over a concentration range from 0.1 pg mL^-1 to 1 ng mL^-1, with a lower detection limit of 33 fg mL^-1 (based on S/N = 3). The proposed biosensor demonstrated the advantages of ultra-sensitivity, high specificity and acceptable reproducibility, suggesting that the proposed strategy has the potential for the quantification of NMP-22 in human urine samples. Moreover, the novel nanocomposite Co-MOFs/CuAu NWs are promising materials for electrochemical sensors to detect other biomolecules.

Vertical Gold Nanowires Stretchable Electrochemical Electrodes

Conventional electrodes produced from gold or glassy carbon are outstanding electrochemical platforms for biosensing applications due to their chemical inertness and wide electrochemical window, but are intrinsically rigid and planar in nature. Hence, it is challenging to seamlessly integrate them with soft and curvilinear biological tissues for real-time wearable or implantable electronics. In this work, we demonstrate that vertically gold nanowires (v-AuNWs) possess an enokitake-like structure, with the nanoparticle (head) on one side and nanowires (tail) on the opposite side of the structure, and can serve as intrinsically stretchable, electrochemical electrodes due to the stronger nanowire-elastomer bonding forces preventing from interfacial delamination under strains. The exposed head side of the electrode comprising v-AuNWs can achieve a detection limit for H₂O₂ of 80 μM, with a linear range of 0.2-10.4 mM at 20% strain, with a reasonably high sensitivity using chronoamperometry. This excellent electrochemical performance in the elongated state, in conjunction with low-cost wet-chemistry fabrication, demonstrates that v-AuNWs electrodes may become a next-generation sensing platform for conformally integrated, in vivo biodiagnostics.

Facile synthesis of 3D N-doped porous carbon nanosheets as highly active electrocatalysts toward the reduction of hydrogen peroxide

Constructing three-dimensional (3D) conductive frameworks with high specific surface areas and porous structures is indispensable for their applications as electrocatalysts. In this work, we illustrate for the first time that 3D N-doped porous carbon nanosheets (3D-NS), which are synthesized via a facile one-pot pyrolysis reaction using glucose and melamine as raw materials, can serve as high performance and green electrocatalysts for the reduction of H2O2. Moreover, a series of 3D-NS samples with a controllable content of nitrogen were obtained by adjusting the calcination temperature. From our research, the 3D-NS obtained at 900 °C possessed high specific surface areas, porous structures, proper dosages of N atoms, suitable degrees of graphitization and defects. Furthermore, we also illustrate their application in H2O2 electrochemical sensing in physiological environments. Under optimum conditions, the 3D-NS-based sensor displays a wide linear scope in the range of 0.5-14 000 μM and a low detection limit of 0.18 μM (S/N = 3). Therefore, with desirable selectivity, stability and anti-interference performance, the proposed sensor can be feasibly applied to detect H2O2 in human serum samples.

Hybridized Polyoxometalate-Based Metal-Organic Framework with Ketjenblack for the Nonenzymatic Detection of H2 O2

The rational design and development of efficient and affordable enzyme-free electrocatalysts for electrochemical detection are of great significance for the large-scale applications of sensor materials, and have aroused increasing research interest. Herein, we report that a typical polyoxometalate (POM)-based metal-organic framework (NENU5) that was hybridized with ketjenblack (KB) was a highly efficient electrochemical catalyst that could be used for the highly sensitive nonenzymatic detection of H2 O2 . The composite catalyst exhibited superb electrochemical detection performance towards H2 O2 , including a broad linear range from 10-50 mm, a low detection limit of 1.03 μm, and a high sensitivity of 33.77 μA mm-1 , as well as excellent selectivity and stability. These excellent electrocatalytic properties should be attributed to the unique redox activity of the POM, the high specific surface area of the metal-organic framework (MOF), the strong conductivity of KB, and the synergistic effects of the multiple components in the composites during the electrolysis of H2 O2 . This work provides a new pathway for the exploration of nonenzymatic electrochemical sensors.

Three-Dimensional Porous Nickel Frameworks Anchored with Cross-Linked Ni(OH)2 Nanosheets as a Highly Sensitive Nonenzymatic Glucose Sensor

A facile and scalable in situ microelectrolysis nanofabrication technique is developed for preparing cross-linked Ni(OH)₂ nanosheets on a novel three-dimensional porous nickel template (Ni(OH)₂@3DPN). For the constructed template, the porogen of NaCl particles not only induces a self-limiting surficial hot corrosion to claim the "start engine stop" mechanism but also serves as the primary battery electrolyte to greatly accelerate the growth of Ni(OH)₂. As far as we know, the microelectrolysis nanofabrication is superior to the other reported Ni(OH)₂ synthesis methods due to the mild condition (60 °C, 6 h, NaCl solution, ambient environment) and without any post-treatment. The integrated Ni(OH)₂@3DPN electrode with a highly suitable microstructure and a porous architecture implies a potential application in electrochemistry. As a proof-of-concept demonstration, the electrode was employed for nonenzymatic glucose sensing, which exhibits an outstanding sensitivity of 2761.6 μA mM^-1 cm^-2 ranging from 0.46 to 2100 μM, a fast response, and a low detection limit. The microelectrolysis nanofabrication is a one-step, binder-free, entirely green, and therefore it has a distinct advantage to improve clean production and reduce energy consumption.

Atomic-Thick PtNi Nanowires Assembled on Graphene for High-Sensitivity Extracellular Hydrogen Peroxide Sensors

H₂O₂ sensors with high sensitivity and selectivity are essential for monitoring the normal activities of cells. Inorganic catalytic nanomaterials show the obvious advantage in boosting the sensitivity of H₂O₂ sensors; however, the H₂O₂ detection limit of reported inorganic catalysts is still limited, which is not suitable for high-sensitivity detection of H₂O₂ in real cells. Herein, novel atomic-thick PtNi nanowires (NWs) were synthesized and assembled on reduced graphene oxide (rGO) via an ultrasonic self-assembly method to attain PtNi NWs/rGO composite for boosting the electroanalysis of H₂O₂. In 0.05 M phosphate-buffered saline (pH 7.4) solution, the as-prepared PtNi NWs/rGO shows an extraordinary performance in quantifying H₂O₂ in a wide range of concentrations from 1 nM to 5.3 mM. Significantly, the detection limit of PtNi NWs/rGO reaches unprecedented 0.3 nM at an applied potential of -0.6 V (vs Ag/AgCl), which enables the detection of traced amounts of H₂O₂ released from Raw 264.7 cells. The excellent performance of H₂O₂ detection on PtNi NWs/rGO is ascribed to the high-density active sites of atomic-thick PtNi NWs.

Aligned copper nanowires as a cut-and-paste exclusive electrochemical transducer for free-enzyme highly selective quantification of intracellular hydrogen peroxide in cisplatin-treated cells

The role and reliable quantification of intracellular hydrogen peroxide during cancer therapy constitutes an unexplored and fascinating application. In this work, we report the fabrication of vertically aligned copper nanowires (v-CuNWs) using electrosynthesis on templates, and their application as a cut-and-paste exclusive and flexible electrochemical transducer. This easily adaptable electrodic platform is demonstrated for a fast, simple and free-enzyme selective quantification of intracellular hydrogen peroxide in Cisplatin-treated human renal HK-2 cells. The v-CuNWs sensor was compared with an HRP-enzyme-based biosensor showing excellent correlation and indicates the good selectivity and analytical performance of the v-CuNWs. This sensing approach opens novel avenues for monitoring cell death processes and shows the potential of H₂O₂ as a cellular damage biomarker, with a clear potency for further developments for in vitro diagnosis and its implication in cancer therapy.

Bioapplications of Electrochemical Sensors and Biosensors

Recent progress in the electrochemical field enabled development of miniaturized sensing devices that can be used in biological settings to obtain fundamental and practical biochemically relevant information on physiology, metabolism, and disease states in living systems. Electrochemical sensors and biosensors have demonstrated potential for rapid, real-time measurements of biologically relevant molecules. This chapter provides an overview of the most recent advances in the development of miniaturized sensors for biological investigations in living systems, with focus on the detection of neurotransmitters and oxidative stress markers. The design of electrochemical (bio)sensors, including their detection mechanism and functionality in biological systems, is described as well as their advantages and limitations. Application of these sensors to studies in live cells, embryonic development, and rodent models is discussed.

Boosted Sensor Performance by Surface Modification of Bifunctional rht-Type Metal-Organic Framework with Nanosized Electrochemically Reduced Graphene Oxide

The surface and interface could be designed to enhance properties of electrocatalysts, and they are regarded as the key characteristics. This report describes surface modification of a bifunctional rht-type metal-organic framework (MOF, Cu-TDPAT) with nanosized electrochemically reduced graphene oxide (n-ERGO). The hybrid strategy results in a Cu-TDPAT-n-ERGO sensor with sensitive and selective response toward hydrogen peroxide (H₂O₂). Compared with Cu-TDPAT, Cu-TDPAT-n-ERGO exhibits significantly enhanced electrocatalytic activities, highlighting the importance of n-ERGO in boosting their electrocatalytic activity. The sensor shows a wide linear detection range (4-12 000 μM), and the detection limit is 0.17 μM (S/N = 3) which is even lower than horseradish peroxidase or recently published noble metal nanomaterial based biosensors. Moreover, the sensor displays decent stability, excellent anti-interference performance, and applicability in human serum and urine samples. Such good sensing performance can be explained by the synergetic effect of bifunctional Cu-TDPAT (open metal sites and Lewis basic sites) and n-ERGO (excellent conductive property). It is expected that rht-type MOF-based composites can provide wider application potential for the construction of bioelectronics devices, biofuel cells, and biosensors.

Graphene Oxide Directed One-Step Synthesis of Flowerlike Graphene@HKUST-1 for Enzyme-Free Detection of Hydrogen Peroxide in Biological Samples

A novel metal-organic framework (MOF)-based electroactive nanocomposite containing graphene fragments and HKUST-1 was synthesized via a facile one-step solvothermal method using graphene oxide (GO), benzene-1,3,5-tricarboxylic acid (BTC), and copper nitrate (Cu(NO₃)₂) as the raw materials. The morphology and structure characterization revealed that the GO could induce the transformation of HKUST-1 from octahedral structure to the hierarchical flower shape as an effective structure-directing agent. Also, it is interesting to find out that the GO was torn into small fragments to participate in the formation of HKUST-1 and then transformed into the reduction form during the solvothermal reaction process, which dramatically increased the surface area, electronic conductivity, and redox-activity of the material. Electrochemical assays showed that the synergy of graphene and HKUST-1 in the nanocomposite leaded to high electrocatalysis, fast response, and excellent selectivity toward the reduction of hydrogen peroxide (H₂O₂). Based on these remarkable advantages, satisfactory results were obtained when the nanocomposite was used as a sensing material for electrochemical determination of H₂O₂ in the complex biological samples such as human serum and living Raw 264.7 cell fluids.

Cobalt phosphide nanowires: an efficient electrocatalyst for enzymeless hydrogen peroxide detection

In this letter, we demonstrate for the first time that cobalt phosphide nanowires (CoP NWs) exhibit remarkable catalytic activity toward electrochemical detection of hydrogen peroxide (H2O2). As an enzymeless H2O2 sensor, such CoP NWs show a fast amperometric response within 5 s and a low detection limit of 0.48 μM. In addition, this nonenzymatic sensor displays good selectivity, long-term stability and excellent reproducibility.